1. Field of the Invention
The present invention relates to liquid-ejection recording heads for ejecting a liquid such as ink in droplet form onto a recording material such as paper, and also relates to methods for producing the liquid-ejection recording heads.
2. Description of the Related Art
A typical liquid-ejection head for use in liquid ejection recording includes fine outlets (orifices), flow channels leading to the outlets, and pressure-generating parts disposed in the flow channels to generate ejection pressure. The pressure-generating parts include pressure-generating elements such as electrothermal conversion elements. The electrothermal conversion elements are supplied with drive signals to cause a rapid temperature rise exceeding the nucleate boiling point of the liquid to be ejected, such as ink. The temperature rise generates bubbles in the liquid to produce pressure for ejecting droplets. The electrothermal conversion elements are supplied with drive signals according to recording information to selectively eject the liquid from the outlets.
Liquid-ejection heads capable of providing high-resolution, high-quality images have been in demand particularly in the field of inkjet recording using ink ejection. It is desirable for such liquid-ejection heads to have droplets of reduced size ejected from outlets and to allow the droplets to be ejected at constant volume and ejection speed.
To achieve such liquid ejection, the specification of U.S. Pat. No. 6,155,673 discloses a method for ejecting droplets by allowing bubbles generated by electrothermal conversion elements to communicate with the outside air. According to this method, the size of droplets ejected depends on the size of outlets and the distance between the electrothermal conversion elements and the outlets (hereinafter referred to as “element-outlet distance”), and therefore fine droplets of nearly the same size can be constantly ejected.
For inkjet recording heads based on the method described above, the element-outlet distance may be reduced to eject finer droplets and thereby create higher-resolution images. Also, the element-outlet distance must be accurately defined with high reproducibility to eject droplets of a desired size.
The specification of U.S. Pat. No. 5,478,606 discloses a method for producing an inkjet recording head with a predetermined element-outlet distance defined accurately with high reproducibility. In this method, a flow channel pattern is formed with a soluble resin on a substrate on which pressure-generating elements for generating ejection pressure are formed. The soluble resin layer is then coated with a solution prepared by dissolving in a solvent a coating resin containing an epoxy resin that is solid at room temperature to form a coating resin layer constituting, for example, channel partitions between the individual flow channels. Outlets are then formed in the coating resin layer. Finally, the soluble resin layer is removed by dissolution.
In addition to higher image resolution and quality, higher throughput is demanded of such inkjet recording heads. To achieve higher throughput, the refilling of flow channels with ink after the ejection of droplets must be accelerated so that ejection frequency (drive frequency) can be increased. The reduction in the flow resistance of ink supply channels leading from an inlet to outlets is desired for accelerated refilling.
Liquid-ejection heads having ink supply channels with reduced flow resistance are disclosed in Japanese Patent Laid-Open Nos. 10-095119 and 10-034928. These publications disclose liquid-ejection heads in which the height of ink supply channels is larger near an inlet than near pressure-generating elements and methods for producing the liquid-ejection heads. According to the methods disclosed in these publications, a portion of a substrate from near the inlet to near the pressure-generating elements is trimmed to relatively increase the channel height near the inlet. This increases the cross-sectional area of the ink supply channels to reduce the flow resistance thereof. Thus, the methods disclosed in these publications propose an effective approach to achieving higher throughput.
For the method disclosed in U.S. Pat. No. 5,478,606, however, simply trimming the substrate more deeply for reduced flow resistance causes the following problem. The soluble resin layer having the flow channel pattern is depressed on a trimmed portion of the substrate, and thus the overlying coating resin layer is thickened on the depressed portion. As a result, the channel height is decreased by the increase in the thickness of the coating resin layer.
On the other hand, increasing the cross-sectional area of the flow channels in the lateral direction thereof, rather than in the depth direction thereof, undesirably poses difficulty in increasing the density at which the outlets are arranged.